When epoxy resins are cured with various curing agents, the resins are turned to cured products which are generally excellent in mechanical property, water resistance, chemical resistance, heat resistance, electric property and others; thus, the resins are used in wide fields of adhesives, paints, laminated plates, molding materials, casting materials and others. The epoxy resin which has been most popularly used hitherto is bisphenol A type epoxy resin. A cured product of the epoxy resin, itself, is insufficient in flame retardancy. Thus, in order to give flame retardancy thereto, a flame retardant or the like has been compounded into the epoxy resin hitherto. Usually, as the flame retardant, a bromine compound, an antimony compound of a flame retardant assistant, or the like is used; there are generally known tetrabromobisphenol A and epoxidized products thereof, a compound obtained by causing tetrabromobisphenol A to react with bisphenol A type epoxy resin, and others. As a curing agent for the epoxy resin, acid anhydrides or amine compounds are known; however, in electric and electronic fields, phenol novolac is used in many cases from the viewpoint of reliabilities such as heat resistance. In recent years, there has been known an example wherein an aromatic polyamide having a phenolic hydroxyl group is used as the curing agent in order to improve the heat resistance and the flexibility (Patent Document 1).
In the meantime, polyimide has excellent heat resistance, flame retardancy, flexibility, mechanical property, electrical property and chemical resistance, and is widely used in electric/electronic parts, semiconductors, communication equipment and circuit parts therein, and peripheral equipment therein. Polyimide resin is slightly soluble in organic solvents; therefore, it is necessary that a polyamic acid, which is a precursor thereof, is painted onto a substrate and next the resultant is heated and dehydrated. At this time, curling based on hardening shrinkage is caused and water is generated. These are problems. In recent years, solvent-soluble polyimide has been developed, and has been used for coating or as orienting films or insulating films (Patent Document 2).
Patent Document 1: JP 2005-29720 A
Patent Document 2: Republication Patent WO2003-060010